Attached algal communities (phytoperiphyton) in the Kovda River and its 18 tributaries were studied, including the analysis of their taxonomic composition, ecology and spatial distribution. In total, 178 species were identified, belonging to Cyanophyta (Cyanoprokaryota) (27), Ochrophyta (121), Dinophyta (1), Rhodophyta (3), Chlorophyta (26). The paper discusses the main principles behind the formation of the structure of phytoperiphyton communities in the rivers. Based on the analysis of the taxonomic composition and structure of phytoperiphyton in the river ecosystems, similarities in the community composition were revealed. The dominant complex is represented by a limited number of species resistant to the dynamic water load. The dependence of changes in the quantities and structural characteristics of phytoperiphyton on the river's hydrological regime is demonstrated. Widespread oligohalobial species that are either acidophilic or pH-indifferent prevail in the ecological-geographical composition of algae. According to the contribution of indicator species, water in the streams and lakes is oligosaprobic, belonging to class II of water purity. Algal abundance and biomass in the waterbodies studied ranged from0.1 to 1310.1・10⁴ cells cm^-2 and 0.01 to 28.4 mg cm^-2.